The present invention relates generally to digital multimeters. More particularly, the invention relates to a digital multimeter having an improved jack detection arrangement.
Digital multimeters (DMMs) function to measure a number of electrical parameters as needed for service, troubleshooting and maintenance. Such parameters may include AC voltage and current, DC voltage and current, resistance and continuity. In some cases, a DMM may measure other parameters such as capacitance and temperature.
A DMM will often be configured as a hand-held unit having a rotary knob by which various functions are selected. A plurality of lead jacks are provided in the case (i.e., housing) of the unit for connection of test leads. The specific jack used may depend on the function that has been selected. An LCD display provides a reading of the tested parameter.
For at least some of the jacks, it is desirable for the multimeter to “know” whether a plug is inserted. This is because the presence of a plug in the jack can create problems if the user has selected certain functions using the rotary knob. Various arrangements have been utilized in the past to detect the presence of a plug. For example, in one such arrangement, the socket in a particular jack has been split into two separate halves. A continuity check across the two halves reveals the presence of a plug. While this arrangement has worked reasonably well, there is room in the art for additional novel arrangements.
Details regarding the construction and operation of multimeters may be discerned from U.S. Pat. Nos. 7,034,517, 6,466,003 and 6,043,640, incorporated herein by reference.